Defend is very similar to the mission attack where the commander instead of attacking a captured firebase, must find the friendly base under attack and then hold of the attacking enemy force. The goal of the mission is to prevent the enemy from reaching the tactical table in the middle of the base. If an enemy reaches the center of the base the mission is a failure. The game at regular intervals prompts how many hostiles are required to be eliminated around the base for the mission to be classed as success. It is important to note that even if the mission is considered as success, if an enemy reaches the tactical table afterwards, the mission still fails.
Mines, grenades, heavy weapons, and fire support (specifically gun ships) and Rangers with high combat and spotting skills are all recommended due to the type of engagement. The enemy force usually is not be very heavy if operating in a low heat AO, but Support Weapons such as SPG-9s, mortars, and DShK's are all possibilities. The Ground Movement Sensor is also very useful for this mission as an enemy may walk directly to the table un-spotted causing the mission to fail. To minimise the failure during extraction, it is suggested to call impromptu extraction directly to the firebase.